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. Guillou et al. J. Exp. Mar. Biol. Ecol. 245 2000 183 –196
1. Introduction
Numerous field and laboratory studies conducted on echinoderms have led to the conclusion that any variation in food supply highly influences the allocation of resources
to somatic and gonadal growth function. Food quality and quantity both affect sea urchin growth reviewed by Lawrence and Lane, 1982. Food limitation slows down growth
rate, and can lead to re-absorption of material from the body wall and a reduction in test
´ diameter Ebert, 1967, 1968; Dix, 1972; Regis, 1979; Levitan, 1988, 1989, 1991.
Different components of somatic growth may also vary like, for example, Aristotle’s lantern which by lower nutrient conditions becomes bigger and larger compared to the
overall body size reviewed by Ebert, 1996. Sometimes, gametogenesis and maturation are also affected under poor nutritional conditions, and may be arrested reviewed first
by Lawrence and Lane, 1982 then, by Xu and Barker, 1990 for asteroids, and Minor and Scheibling, 1997 and Russell, 1998 for strongylocentrotid sea urchins. But most of the
authors have not considered the effect of the reproductive state on the expression of the observed responses; indeed, it is likely that variations in food ration affect energy
partitioning in a way which depends on the reproductive state. As little information is available on this subject, several questions remain: i During the gonad maturation of
sea urchins can a larger ration of food increase the somatic growth rate usually reduced during this stage of biological cycle reviewed by Guillou and Michel, 1994? ii Can it
produce gonadal growth in the post-spawning phase, i.e. a build up of storage reserves? iii Lastly, how will starvation act on somatic and gonadal growth over these different
reproductive periods?
In an attempt to answer to these questions, and with the aim of understanding the patterns of energy allocation to growth and reproduction functions over an annual cycle,
several laboratory experiments were conducted on fed and starved urchins before and after their spawning period. The sea urchin, Sphaerechinus granularis
, was chosen because of its large number in the Glenan Archipelago Southern Brittany, France and
of previous studies dealing with its reproductive cycle in Brittany. Its annual cycle of gonadal growth is characterised by a short breeding season in spring, usually within the
end of March and May, which depends on the seawater temperature during the gonadal growth before spawning Guillou and Michel, 1993. This brief breeding season is
followed by a fast post-spawning recovery concomitant with the development of nutritive tissue in the gonads Guillou and Lumingas, 1998. A long mature stage
extends from autumn to early spring with a possible decrease in gonad index attributed to the use of reserves whenever seawater temperature is abnormally low. The
comparisons of various populations of this species living in different areas Mortensen, 1943; Keckes in Fenaux, 1972; Semroud and Senoussi, 1989; Soualili, 1998 have
shown that environmental conditions such as food supply and the ‘energy reserves to generate mature gametes’ Cochran and Engelmann, 1975 highly control the gonad
volume whereas seawater temperature acts more on the reproductive cycle chronology than on the fecundity rate Guillou and Michel, 1993; Guillou and Lumingas, 1998. A
better understanding of nutrient use and allocation to different body components over the reproductive cycle could lead to ways of increasing the somatic and gonadal growth of
this potential aquaculture species.
M . Guillou et al. J. Exp. Mar. Biol. Ecol. 245 2000 183 –196
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2. Materials and methods
